Getting Cannot redeclare class modIMuser - Joomla! Forum - community, help and support

i working on small module , coming across error:

cannot redeclare class modimuser in g:\webserver\htdocs\sns\modules\mod_whosonline\helper.php on line 16

not sure why class modimuser declared once in helper file , not in other file.
here code have error affecting.

code: select all

class modimuser
{
   function getusers()
   {
       $db      =& jfactory::getdbo();
      
      $query = 'select distinct a.username' .
             ' #__session a' .
             ' client_id = 0' .
             ' , a.guest = 0';
      
   }

}

any great. area calls class , function following:

code: select all

$users = modimuser::getusers();

to display default.php this:

code: select all

<li><strong><?php echo $users; ?></strong></li>